This invention relates to terrain imaging using coherent beam radiation. It is usable to detect short range objects and determine the movement of the objects. It can be used by a blind person to avoid running into obstacles. Law enforcement and security personnel can use it to detect the location and movement of persons which are not visible to the eye such as at night.
In the last several decades, several electronic techniques have been tried to develop methods to image the near field terrain of an area for circumnavigating through and around obstacles and for protection against intrusion of an area. These methods have suffered from a common problem of poor resolution and false information or images as a result of background objects moving, such as leaves blowing, birds flying or small animals.
One of the technologies employed for intrusion detection or for terrain imaging has been ultrasonics. An ultrasonic acoustical signal is transmitted into space is reflected from objects in the near field to the transmitter. By ascertaining the return signal level or by measuring the time delay, you can infer a range of the object from the transmitter to the receiver.
A primary problem with the ultrasonics is the very low resolution of distinguishing objects. This is a result of the difficulties in focusing the ultrasonic sound waves into a small beam that doesn't disperse. The relatively low resolution of an image by such a method makes it of less value to the user in trying to circumnavigate himself through an area of obstacles. When this method is used for intrusion detection, the low resolution is not the only problem. Ultrasonics is very susceptible to motion from blowing bushes, plants or small animals moving about. These objects, when in the field of view, tend to give a high number of false alarms. Other technologies have attempted to use light or microwave emissions to detect the presence of objects, but have relied largely on the return signal strength or on triangulation to determination what the range is to the reflecting objects. These methods of range determination suffer from low resolution since triangulation can only be used for a very near field. Signal strength is subject to other sources of errors, in particular, the type of target light hits and hence the amount that is reflected back.
The inability to resolve accurate ranges well as the azmith of those ranges have made these methods of limited value. Failure to use computational devices to interpret what image is generated has further reduced the effectiveness of these methods.
One type of light intrusion detection that has been used successfully and extensively is the photo-electric beam devices. These devices require some sort of an inflector that is the receiver at the end of a light beam to operate. This method has not been used for scanning but does not produce any accurate image of the surrounding terrain. Furthermore, this method does not provide range information about intrusions.
Methods of passive infrared emissions have also been used for intrusion detection and for a means to avoid obstacles. These methods do not provide good range information and provide no azmith information and do not generate good images.
Video based systems by their very nature provide a very high definition image. However, translating this image information into a format usable by the blind or by a computer is a problem of great complexity. While it is possible to use video systems for motion detection in an intrusion scenario, they are plagued by high false alarm rates since any change in light causes an alarm signal. This method generally requires a stable closed environment in which to work. Thus, a method that can provide moderate resolution image of only 2 dimensions provides a means that can easily be interpreted by computational methods or by the blind, who can only process a limited amount of stimuli, and interpret as an image.
An object of the invention to provide a method and apparatus which can be used by a blind person to ascertain obstacles and to indicate the location and movement of the obtacles.
Another object of the invention to provide a method and apparatus which can be used by any person at night to ascertain obstacles and to indicate the location and movement of the obtacles.
Another object of the invention to provide a method and apparatus which can be used to ascertain short range obstacles and to indicate the location and movement of the obtacles.
Another object of the invention to provide a method and apparatus which can be used to ascertain obstacles and to indicate the location and movement of the obtacles in security monitoring situations.
Other objects of the invention will be apparent from the specification and claims.